What is "mermaid fish"

Mermaid \Mer"maid\, n. [AS. mere lake, sea. See Mere lake, and maid.] A fabled marine creature, typically represented as having the upper part like that of a woman, and the lower like a fish; a sea nymph, sea woman, or woman fish.

Note: Chaucer uses this word as equivalent to the siren of the ancients.

Mermaid fish (Zo["o]l.) the angel fish ( Squatina).

Mermaid's glove (Zo["o]l.), a British branched sponge somewhat resembling a glove.

Mermaid's head (Zo["o]l.), a European spatangoid sea urchin ( Echinocardium cordatum) having some resemblance to a skull.

Mermaid weed (Bot.), an aquatic herb with dentate or pectinate leaves ( Proserpinaca palustris and Proserpinaca pectinacea).